Receiving apparatus for communication systems for railway trains



June 1, 1937; A SORENSEN 2,0821% RECEIVING KPPARATUS FOR' COMMUNICATION SYSTEMS FOR RAILWAYTRAINS Filed May 5, 1934 Hz g1? Frequency Audio Amplzfe'er' and Fppquenog Demodulazor Amplefibn v JNVENTCR Andrew J. Sorenmn BY 6221M HIS ATTORNEY Patented June 1, 1937 qUNlTED STATES RECEIVING APPARATUS FOR COMIMUNICA- TION SYSTEMS FOR RAILWAY TRAINS Andrew J. Sorensen,

Pittsburgh, Pa., assignor to The Union Switch & Signal Company,

Swissvale, Pa., a, corporation of Pennsylvania Application May 5, 1934, Serial No. 724,132

1 Claim.

My invention relates to receiving apparatus for communication systems for railway trains, and has for an object the provision of novel and improved receiving apparatus for systems of the type referred to wherewith satisfactory reception of either a telephone message or a code message aboard a train is assured, and which is effective to eliminate noise.

I will describe one form of apparatus embodying my invention, and will then point out the novel features thereof in the claim.

For a better understanding of my invention reference may be had to the accompanying drawing which is a diagrammatic View of one form of receiving apparatus embodying my invention as preferably provided at location aboard a railway train. As the specific structure of the high frequency amplifier and demodulator and also of the audio frequency amplifier forms no 20 part of my present invention, these devices are illustrated conventionally only for the sake of simplicity, and it will be understood that each of these devices may be any one of several types well-known to the art. Likewise, the band-pass filter BPF interposed ahead of the audio frequency amplifier is illustrated conventionally as its specific structure forms no part of my present invention, and any one of several forms may be provided as desired,- it being understood that this filter is proportioned and adjusted to pass the voice frequencies after demodulation. The band-pass filter BPFI interposed ahead of the high frequency amplifier is also shown conventionally and may be any one of several forms. It is deemed sufficient for the present specification to point out that this filter BPFI is so proportioned as to pass the upper side band frequencies of the carrier having a width equal to the voice frequency range with little attenuation and to substantially suppress frequencies either above or below this range. As commonly provided, such input filters are of relatively elaborate networks in order to obtain elimination of noise frequencies and elimination of frequencies from unwanted sources. However, as will appear more fully'hereinafter, with apparatus embodying my invention input filters of relatively simple network would be employed or the filter would be omitted altogether.

In such communication systems for railway trains it has been proposed to attach to the microphone of the transmitting equipment, and which microphone is indicated on the drawing by the reference character M, an operating handle 5 through the medium of which the operator can select the receiving or transmitting condition of the equipment as desired. As here shown, the handle 5 is adapted to be manually operated to any one of three positions indicated by dotted lines and which positions I shall designate as normal, communication and code. As shown schematically, a circuit controlling contact I0 is operatively connected with the handle 5, and is moved to the three respective positions identified by the numerals l, 2 and 3 in response to the normal, communication and code positions of the handle 5. Mounted on the handle 5 is a common spring return push button 8, which, when released, makes engagement with a contact I! and which is forced out of engagement therewith when depressed. The arrangement is such, as will appear hereinafter, that the receiving equipment is set to receive a code message in the normal position of the handle 5, and is set to receive a telephone conversation with the handle 5 moved to the communication position and the push button released. The sending of a telephone current is accomplished under the communication position of the handle with the push button depressed and the sending of a code current is accomplished under the code position of the handle. The transmitting of current being no part of the apparatus of the present application these last two conditions of the handle 5 and push button 6 will not be further described.

A relay R. is associated with the handle 5 and push button 8 by the relay being provided with an energizing circuit which includes the contact [0 and the push button 5. It will beclear from an inspection of the drawing that with the handle 5 occupying either the normal or the code position and the contact It, thus occupying either its No. l or No. 3 position, the circuit is open and the relay R is deenergized, but that ifthe handle 5 is moved to the communication position and thecontact I0 occupies its No. 2 position and the push button 6 remains released, the circuit is closed for supplying current to the winding of the relay R and that relay is picked up. The function of the relay R will appear as the specification progresses.

RC indicates a receiving coil mounted on a Vehicle of a train at any convenient position in inductive relation with the trafiic rails or with the line wires, or it may consist of different portions which are mounted in inductive relation with the rails and line wires, respectively. That is to say, the receiving coil RC is mounted on the vehicle in a position to be effectively infiuenced by current flowing in the traffic rails or in the line wires or in both. Preferably the receiving coil RC will be of relatively large cross section and of the air core type. For coupling the receiving coil RC with the input of the bandpass filter BPFI and thence with the input circuit of the high frequency amplifier, I provide a resistor RI, a capacitance C and a reactor R2, this latter preferably including the primary winding of a transformer T, the secondary winding 23 of which is included in the input side of the band-pass filter BPFI or is included in the input circuit of the high frequency amplifier in the event the filter'is omitted. The lower terminal of the receiving coil RC is connected with the lower terminal of the reactor R2 over a wire I2, and the top terminal of the receiving coil RC is connected with the reactor R2 over resistor RI, capacitance C, wire I 6, back contact ll of the relay R and thence over wire l8 to a tap IQ of the reactor R2, the arrangement being such that only a relatively small portion of the reactor is included between the tap l9 and its lower terminal. In shunt with the resistor RI is a short-circuiting path including wire l3, back contact M of the relay R and a wire l5, while the top terminal 20 of the reactor R2 is connected with a front contact 2| of the relay R over a wire 22. It follows that with the relay R deenergized, the receiving coil RC is included in a receiving circuit which passes from the top terminal of the coil RC along wire l3, back contact M of the relay R, wire l5, capacitance C, wire l6, back contact I! of the relay R, wire l8, mid terminal l9 of the reactor R2, the lower portion of the reactor and wire I2 to the lower terminal of the receiving coil RC. When the relay R is energized and its back contacts l4 and I! are open and its front contact 2i is closed, the receiving coil RC is included in a second receiving circuit which can be traced from the top terminal of the coil RC over resistor RI, capacitance C, wire l6, front contact 2| of the relay R, wire 22, terminal 20 of the reactor R2, the larger portion of the reactor R2 and thence by wire l2 to the lower terminal of the receiving coil RC. The parts are so proportioned that with the relay R deenergized and the receiving circuit including the receiving coil RC, capacitance C and only the lower portion of the reactor R2, the circuit is tuned'to resonance at the code frequency which may be, for example, 7800 cycles per second. Since the receiving coil RC is preferably of theair core type, it can be constructed to have a very low power factor, and this last mentioned receiving circuit will be sharply tuned to pass only a very narrow band of frequencies, that is, it will pass only frequencies a few cycles on either side of the code frequency of 7800 cycles, and hence only a very small amount of frequencies that produce noises in the loud-speaker will be passed. Consequently, during non-transmitting periods and the normal condition of the receiving circuit, very little voltage which will produce a noise will be passed to the band-pass filter BPFI, and, in turn, to the high frequency amplifier, and this input filter may be one of comparatively simple construction. When a code message is received, the receiving circuit will pick up such current at relatively high sensitivity and very little interfering noise voltages will be passed at the same time. Being sharply tuned, this normal receiving circuit will be highly selective with regard to unwanted frequencies which may be sent out by nearby trains other than those with which communication is desired.

In telephone communication systems for railway trains it is customary to first transmit a code calling signal preparatory to telephone communication. Upon reception of such a code calling signal the operator at the receiving location will move the handle 5 to its communicating position and for receiving a telephone conversation will leave the push buttoni released. Under this condition of the handle 5 and the push button 6 the relay R will be picked up. The receiving circuit will now include the receiving coil RC, resistor RI, capacitance C and the larger portion of the reactor R2. The resistor RI is so proportioned that when it is inserted into the circuit the power factor of the'circuit is relatively high and the circuit is broadly tuned to resonance at frequencies extending from 7500 to 9500 cycles, that is, it will pass the upper side band corresponding to a carrier of 7000 cycles modulated at voice frequencies. Under this lat ter condition of the receiving circuit, reception of speech is obtained. Although the broadening of the tuning of the receiving circuit will permit the picking up of more frequencies that produce noise, I have found that with proper volume control for the high frequency amplifier the noise will ordinarily be held at a permissible lever during conversation.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claim Without departing from the spirit and scope of my inven-,

tion.

Having thus described my invention, what I claim is: V

In a railway train signal receiving equipment consisting of an amplifier-demodulator and a loud-speaker for reception of modulated carrier current the combination comprising an air core type receiving coil mounted on a train, a traincarried relay, a resistor, a capacitance, a winding, means for connecting a portion of the winding and the capacitance across the terminals of the receivingcoil including a first back contact of the relay shunting around the resistor and a second back contact interposed between the capacitance and the winding for picking up a code message consisting of impulses of the carrier modulated at a given single frequency; other means for connecting a diflerent portion of the winding, the capacitance and the resistor across the terminals of the receiving coil including a front contact of the relay for picking up a tele phone message consisting of the carrier modulated at voice frequencies; a circuit for energizing said relay including a manually operated contact, and means for coupling said winding with the input circuit of the amplifier.

ANDREW J. SORENSEN. 

